Metal content in carbonaceous ores was first discovered by the inventor herein. By techniques of the first embodiment of the present invention, surface tablelands, alluvium and moraine samples of black carbonaceous ores from Idaho, Nevada and California were assayed, reporting respectively tangible, visible metals in the following amounts: (a) 18.2 ounces of gold per ton; (b) 8.35 ounces of gold per ton and 40.2 ounces of silver per ton; and (c) 32.7 ounces of gold per ton and 90 ounces of silver per ton. The latter samples were from black carbonaceous tailings from the days of the '49ers. Many zero and low value carbonaceous ores and vast areas of low-grade gold-containing carbonaceous ores in the Pacific Northwest were found; however, even these ores were richer in gold than the world's best ore from conventional inorganic ores. Exploitation awaits this low-cost, ecologically safe process. Thus, vast new resources in gold and most other metals may be recovered by means of the present invention. The probable location and extent of sea and land carbonaceous ores was determined throughout the world. Carbonaceous land ores are found in western Canada, the United States, South America, South Africa and Eastern Australia, all of which areas are near the impact edges of the respective dispersing continents, where shallow seas were drained as the continents rose to form plains and impacted to form mountains. Live sea ores are found in quantity in the Philippine estuaries and in Lake Maracaibo. Sea carbonaceous ores are also found in trace to large quantities in shallow estuaries within a band around the earth, approximately 40.degree. latitude on either side of the equator.
All known processes for recovery from these ores have been tried. None were found to be adaptable to the recovery of metals from carbonaceous ores. Early in 1966 the inventor herein filed a United States patent application, the invention of which provided for the first time the quantitative recovery of metals from carbonaceous ores. This process, although it is now used commercially, was primarily an electrolytic leaching method, having a relatively long retention time for extraction. Retention time in the final phases of the invention hereof, however, is less than five seconds and has been found to recover all sought metals quantitatively.
The aforementioned slower electrolytic process was left with full power on. The electrolyte went from the hypochlorite level to the chlorate level of oxygen carrier production. Spontaneous combustion occurred, driving the metals in the carbonaceous ore concentrate into the vapor phase in the form of their compounds, mostly oxides, some sulphides, chlorides, etc. Because of variations in input composite ore make-up and the variations expected in output demands, on-line computer process control may be beneficial for commercial implementation of the present invention, if other than noble metals are to be recovered.
As previously indicated, chlorine, hydrogen, oxygen and ozone gases may be used. Ozone and fluorine, two oxidants stronger than oxygen carrying chemicals, have been tried in the present process, but have been less satisfactory than other oxidants, either because of economics or because no vessel could be found for containment of the reaction except in wet foam, suggesting that organic or inorganic dried foam may be used to contain those gases. Other oxidizing agents, such as hydrogen peroxide and oxygen and chlorine clathrates have been tried and it has been found that under present techniques they must be used wet. The principles used in the present invention combine the scientific disciplines of propellant design, ballistics and mining, which achieve a homogenous reaction of solids, liquids and gases in various combinations approaching that of two gases. In the particulate plasma process described herein, particles are burned "from the inside out", as contrasted with, for example, fluidized bed reactions where burning is "from the outside in". The particulate plasma process takes place invariably as an oxidizing rather than as a reducing reaction, producing net energy in a form easily converted to power, as well as producing much-needed metals. Accordingly, the energy by-product may be harnessed and used.
The particulate plasma process may be sandwiched between conventional beneficiation or flotation and smelting and conventional refining for land carbonaceous ores. Existing sulfide ore processing facilities, now being abandoned because of the cost of implementing the new ecology laws, can be rebuilt to process carbonaceous ores using the particulate plasma process or arc process as is herein disclosed, thereby also rendering these plants ecologically safe as well as salvageable. The value of the metals which may be recovered at relatively little cost will permit such mine sites to be restored.
A mixture was prepared of pure graphite and oxygen carrying chemicals, nitrates and others in wet solution plus a wetting agent to penetrate the graphite with oxygen carrier. Upon drying this intimate mixture and heating to above 400.degree.C, the particles go into brilliant auto-combustion with sufficient energy released to drive all contained metals into the vapor phase as metals and/or metal compounds safely and efficiently. Graphite represents the extreme refractory condition of the reducing agent, i.e. the carbonaceous ore concentrate. One would not be likely to encounter anything quite so refractory as pure graphite in actual production.
The present invention relates to methods for mineral recovery, and in particular, to methods wherein precious and base metals are recovered from composite ores in underwater offshore deposits -- principally organic silts and the like, and land carbonaceous ore deposits usually metamorphosized from these same types of sea ores over a period of several hundred million years. The values are recovered by separating the composite metal and organic materials which comprise these submarine carbonaceous silts from the sand and shells also present therein or their derivatives, the silicates, carbonates, etc. from equivalent land carbonaceous ore deposits. The material is frothed in an aqueous medium forming an organic gel from the organic composite materials by the addition of oil and/or surface active agents in flotation. Part of the water is then removed and substantially all of the oil and/or surfactants. Next the carbonaceous residues or float are strongly oxidized by one of the following methods:
1. In accordance with the first embodiment, a liquid oxidant may be used, such as perchloric acid trihydrate. The mixture is then heated to achieve spontaneous ignition and combustion of the composite material to eliminate the organic portion thereof and produce an ash comprised of noble and base metals and slags. The ash is then suitable for assay, preferably by fire assay.
2. A liquid oxidant may be used, such as perchloric acid dihydrate, again following the first embodiment. This permits spontaneous ignition of the necessarily high carbonaceous composite material used in this method to eliminate the organic portion thereof and to volatilize all noble and most base metals into the vapor phase and to produce an ash comprised chiefly of alkali and alkaline-earth metal oxides barren of nobel metals.
3. Since the first embodiment is used primarily to remove completely organic materials from a sample to be assayed and the second embodiment is unusable in conventional assay and is possibly too expensive for production, a solid oxidant in concentrated solution may be used, in accordance with the second, third and fourth embodiments, with wetting agents or with high pressure to assure penetration of the oxygen carrier into the porous carbonaceous particles. Excess oxidant is then removed. The intimate mixture is then dried and ignited, driving all sought metals into the vapor phase as metals and/or metal compounds. This is known as the "particulate plasma" method. The metal vapors are recovered from the vapor phase by fractional condensation and electrostatic precipitation, producing substantially separate metal and compound concentrates of approximately 50% metal by weight.
Further, the second, third and fourth embodiments lend themselves to the use of composite electrodes to provide an arc of electricity to drive metals into the vapor phase as metals and/or metal compounds, using both electrical and chemical action to ignite the mixture to provide continuing energy to vaporize the carbonaceous concentrate, natural or synthetic into the vapor phase. Condensation from the vapor phase is done as described hereinabove. The choice of energy to drive metals into the vapor phase may range from total arc energy to total chemical energy, except for ignition which is of course by electric arc in this mode. Economic and process considerations favor chemical energy. For ignition, arc power is initially at a high level. Thereafter, it need be sustained only at very low power, the continuing energy deriving largely from chemical reaction.
The same general results may be brought about by the substitution of certain variables which will be set forth in further detail herein. These include methods of separating the inorganic material from the composite material and the manner in which combustion or ignition of the composite material takes place.
Silt and other submarine deposits, as well as landlocked sedimentary carbonaceous deposits, include noble metal values, particularly gold, silver and platinum, since these metals do not go back into solution as readily as do more easily oxidized base metals, especially when such silts or deposits are from certain geographical regions.
Some techniques for evaluating the amount of precious and other metals present in carbonaceous ore have often, by their nature, either destroyed or masked the presence of such materials or rendered it difficult to determine accurately the amounts of such materials actually present. A prime reason is that graphitic formations occur which are refractory to melting and conventional processing. In other words the assaying techniques used have often either been based on the assumption that the precious metals were present in some particular form, which has not always been the case, or have been based on the assumption that such metals, if present, would undergo certain characteristic chemical reactions. However, it has been found that certain of these assumptions and theories have been fallacious, and, as a result, noble metals have escaped notice when the ore material in question has been analyzed with a view toward detecting the material, i.e., graphitized fractions slag out and do not burn or melt to provide metal. For instance also, atomic absorption or neutron activation assay techniques, the known standard techniques for determination of unknown content, are very unreliable or may not be used at all for this type of ore.
In other techniques, although the presence of gold or other valuable metals might be established, the methods suggested for use in recovering the metal were similar in concept, if not in execution, to the assay techniques used to determine the presence of the noble metals. Consequently, since a number of prior art processes of assaying were not economically feasible for commercial production, recovery of metal values, even of metal values known to be present, was not attempted, or, if attempted, was not successful commercially.
The present invention, on the other hand, is based in part upon the assumption that many precious metal values are extensively present in certain ores, including underwater silty organic residues and inland sedimentary deposits or carbonaceous land ores equal to relict carbonaceous sea ores. The metals, if not in actual chemically or physically precise forms of complex organic compounds, are at least present in such compounds and can therefore be recovered by an appropriate process, which have in large part escaped detection and/or recovery by techniques of the prior art.
These assumptions have been reinforced by exploration work throughout the world by the United States Bureau of Mines, by the United States Geological Survey and by assays made of these ores. Accordingly, in view of the general state of the prior art of precious metals recovery, and particularly in view of the drawbacks associated with prior art efforts to recover metal values from underwater deposits and other sedimentary deposits or their equivalent land deposits, it is an object of the present invention to provide an improved precious metal recovery method including the recovery of most base metals as well.
A further object is to provide a metal recovery method in which underwater deposits and their land counterparts are separated into noble metal-bearing components and waste components. Metal-bearing components are washed or treated with a water-immiscible organic cleaning-flotation agent in slightly acid solution to recover, almost completely all of the organic components as float.
Another object is to provide a method in which a metal-bearing composite material is recovered in a form suitable for subsequent treatment by formation into a gel-like material or float from which the carbonate content has been removed by chlorine or acid and thereafter by removing the water-immiscible, cleaning, flotation organic agent from the gel-like or float material.
Another object is to provide a method wherein a partially dried, metal containing composite material is treated solely with a strong oxidizing agent, or with a strong oxidizing agent where the carbonate content is not removed.
A still further object of the present invention is to provide a metal recovery method in which oxidized composite material having a noble metal component and an organic component is treated to remove excess oxidizing agent. Thereafter at an only moderately high temperature, the treated material spontaneously ignites and burns to form an ash containing recoverable noble metal compounds suitable for eventual recovery of metal therefrom.
Another object of the present invention is to provide a method for treating a floating constituent of an ore material with a water-immiscible, cleaning and floating agent in which the water supporting the composite material layer is slightly acidified, in which a significant portion of the solvent is recovered in a dryer, in which the remaining material is treated with a strong oxidizing agent, in which the excessive oxidizing agent is thereafter removed and in which the thus treated material spontaneously ignites and the residue, both coarse and fly-ash material, is collected for reduction to elemental metal form.
A further object is to provide a method in which only minimum quantities of reagents, such as cyanides and fluorides are used in which method the materials are economical and easy to obtain. Ozone (O.sub.3) is not economical and/or workable to use in the dry state but may occur incidentally with other oxidizing agents used, always in atmospheric arc.
A still further object is to provide a method making use of flotation separation of metal containing composite materials from inorganic wastes, hydrocarbon treatment of these materials, and utilization of a dryer for recovering the hydrocarbon, a spraying unit or the like for oxidizing treatment of the composite material, and a dryer and ignition unit for recovering excess oxidizing agent and certain combustion products of the treated composite material, as well as a conveyor or the like for moving the material from one station to another and means for recovering the combustion products of the material for further treatment thereof.
A still further object of the present invention is to provide a method of concentrating valuable metal containing chemically composite materials prior to treatment thereof for recovery of the metal values therefrom.
Another object is to provide a method of concentrating the composite materials before processing thereof by means of successively treating the same in the presence of water with various detergent materials in a desired sequence, following which the composite material is floated and collected in a concentrated form for further treatment.
A still further object is the treatment of the composite material and the remainder of the ore with detergent materials in a predetermined sequence, while, at the same time, mechanically agitating the mixture to accelerate the rate of separation of inorganic materials from the composite material.
A further object is to provide a method of recovering metal values from chemically composite materials, which includes collecting the residues from the combustion of the composite organic materials, and separating the metal values from one another either by first separating the oxides, metals and compounds from one another or by reducing the oxides or other compounds as a group and subsequently separating the metals from one another following the reduction of the oxides and compounds to elemental metal form.
Another object is to provide a method of recovering valuable metals from composite materials which provides for the formation of composite materials adapted to undergo combustion under controlled oxidizing conditions, but which method utilizes a minimum proportion of expensive oxygen-bearing compounds.
Another object is to provide a method of recovering metal values, which includes preliminary separation of an organic or composite pulp from entrained or associated inorganic materials, by applying ultrasonic energy to a mixture of such organic, inorganic and composite materials and water.
Another object is to provide a method of recovering metal containing residues from combustion which includes treating a composite material with an oxidizing agent and a fuel material, and burning the composite material, the oxidizing agent and the additional fuel simultaneously in the presence of air under controlled conditions.
Another object is to provide a method wherein composite, noble metal containing materials may be treated by the addition thereto of combustible organic products, and wherein the composite materials and the added combustible products may be oxidized together, with a part of the oxygen for combustion being supplied from oxygen-bearing treating compounds and the remainder from the atmosphere in which combustion takes place.
Another object is to provide a method of controlling the combustion of noble metal containing composite materials so as to minimize or eliminate the production of refractory products and maximize the yield of reducible, unprotected metal, oxide and compound products resulting from controlled combustion of the composite materials.
A further object is to provide a method of burning together valuable metal containing composite materials and associated fuels, where necessary, so as to minimize the production of unoxidized, high temperature resistant materials created by the combination of unduly high localized combustion temperatures and insufficient oxidizable materials and/or oxidizing agents.
These objects, and other inherent objects and advantages of the invention are attained by separating the chemically composite materials from associated ore material, including inorganic components. When these inorganic components have high assay valves, they usually comprise inorganic ores or oxidized carbonaceous ores. They may be partly reconstituted with carbon, graphite or solid hydrocarbon, such as coal. This solid carbon or hydrocarbon is preferably added as fine powder before solid oxygen carrier is applied in solution with a wetting agent or pressure and then dried. Full reconstitution is accomplished by adding a high initial point hydrocarbon to the non-carbonaceous composite material in stoichiometric balance. The natural carbonaceous composite concentrate and the reconstituted or synthetic "carbonaceous" composite concentrate may be considered to be equal, singly or combined.
The composite concentrate may have added to it stoichiometric amounts of gaseous or liquid or solid oxygen carrier applied in solution with a wetting agent or under pressure. It is then dried and heated to ignition and autocombustion in a kiln or be electric arc if the composite concentrate plus oxygen carrier is further compounded with graphite and binder into electrodes. In either case, reducing fractions are consumed, releasing great energy as heat, thus driving contained metals into the vapor phase as metals and/or metal compounds. All reactions must be oxidizing rather than reducing during combustion into particulate plasma. If energy is not minimally sufficient to drive metals into the vapor phase as compounds, the reducing fractions of the composite concentrate are still consumed, but the metal values must then be recovered from the ash by fire assay procedures or by electric arc, furnace, or by other prior art refining technique. If the energy generated is sufficient to drive all sought metals into the vapor phase, the vapor alone will constitute the valuable output and the ash is barren of sought metals.
Metals and compounds are recovered from the vapor phase by fractional condensation in cyclones, scrubbers and electrostatic precipitators. Recovery is essentially by metals or metal groups with minimum overlap to be determined by the number of cyclones and scrubbers in series. These metals are suitable for subsequent collection or reduction to the metals which formed the metal constituent of aforesaid composite materials, natural or reconstituted.
The manner in which this invention achieves its objects and other inherent objects and advantages will become more clearly apparent when reference is made to the accompanying detailed description of the preferred embodiments of the invention, and to the drawings forming a part hereof, in which like reference numerals indicate corresponding parts throughout.